For which value of kkk is the matrix M=(k2510)M = \begin{pmatrix} k & 2 \\ 5 & 10 \end{pmatrix}M=(k5210) singular (non-invertible)?
k=1k = 1k=1
k=2k = 2k=2
k=4k = 4k=4
k=5k = 5k=5